Telnet is a client/server application that allows you to log in to remote devices to manage and maintain the devices.
Large numbers of devices need to be managed and maintained on a network. You cannot connect each device to a terminal. When no reachable route exists between remote devices and a terminal, you can use Telnet to log in to the remote devices from the device that you have logged in to.
As shown in Figure 1, you can use Telnet on the PC to log in to the Telnet client. Because the PC does not have a reachable route to the Telnet server, you cannot remotely manage the Telnet server. To remotely manage the Telnet server, use Telnet on the Telnet client to log in to the Telnet server.